Atrial and ventricular demand pacer having wide range atrial escape interval

ABSTRACT

There is disclosed an atrial and ventricular demand pacer in which the atrial escape interval can be set to be less than 50 percent of the ventricular escape interval without multiple stimulations of the atria between ventricular beats. The atrial pulse generating circuit is triggered upon the occurrence of each ventricular beat, a single atrial stimulating pulse then being generated unless another ventricular beat is first detected within the atrial escape interval. Because an atrial stimulating pulse requires a trigger (ventricular beat), only one atrial stimulating pulse can be generated after each ventricular beat.

United States Patent [19 1 Berkovits et al.

[ Oct. 30, 1973 [54] ATRIAL AND VENTRICULAR DEMAND PACER HAVINGWIDE-RANGE ATRIAL Primary Examiner-William E. Kamm ESCAPE INTERVALAttorneyWilliam C. Nealon et al.

[75] Inventors: Barouh V. Berkovits, Newton Highlands; Robert A.Gulllette, [57] ABSTRACT M th b th f M 6 0 0 ass There IS disclosed anatrial and ventricular demand Assigneei American Optical COPPOIatiOII,pacer in which the atrial escape interval can be set to Southbridge,Mass. be less than percent of the ventricular escape interval withoutmultiple stiinulations of the atria between [22] Filed 1972 ventricularbeats. The atrial pulse generating circuit is [21] Appl. No.: 233,135triggered upon the occurrence of each ventricular beat, a single atrialstimulating pulse then being generated unless another ventricular beatis first detected g 128,419 2 1 within the atrial escape interval.Because an atrial I stimulating pulse requires a gg (ventricular beat),[58] Field of Search 128/419 P, 42], 422 y one atrial Stimulating pulsecan be generated 5 References Cited after each ventricular beat.

UNITED STATES PATENTS 5 Claims, 2 Drawing Figures 3,595,242 7/1971Berkovits 128/419 P 3,593,718 7/1971 Krasner et al. 128/419 P 3,253,5965/1966 Keller, Jr 128/419 P "5 L4 22 r! 20 L3 J J I 1 I11 L 7 27 Ta a[L2 9 keg n) 9 -Tl2 T15 9/ 56 2 -a2 E4 74 J 93/ 96 TM PATENTEBBBI 30 msSHEET 2 BF 2 l e28 \1 m N@ Na 5 Q J n 8 w 8 a m NULW NM. rm M 6 n w? IIJ8 m wn I. 3 W Efi mu I? im m.

3 E mw W T wLm @N a T w ATRIAL AND VENTRICULAR DEMAND PACER HAVINGWIDE-RANGE ATRIAL ESCAPE INTERVAL This invention relates to atrial andventricular demand pacers, and more particularly to such pacers in whichat most one atrial stimulating pulse is generated for each ventricularbeat.

In my co-pending application Ser. No. 214,218 filed on Dec. 30, 1971,which application is hereby incorporated by reference, there isdisclosed an improved synchronized atrial and ventricular pacer. Each ofthe atrial and ventricular pulse generating circuits functions togenerate a stimulating pulse a respective predetermined time intervalafter the last ventricular beat. The ventricular escape interval (thetime period between successive ventricular beats) is longer than theatrial escape interval (the time period between successive ventricularand atrial beats) so that an atrial stimulating pulse, if one isrequired, will be generated before a ventricular stimulating pulse, ifone is required, Each detected ventricular beat controls the resettingof both pulse generating circuits. In the presence of 60-1-12 noise,both pulse generating circuits operate in a continuous mode, as opposedto a demand mode. In such a case, whenever a ventricular stimulatingpulse is generated not only does the ventricular pulse timing circuitrestart, but so does the atrial pulse timing circuit. Thus, even in thepresence of noise the atrial pulse generating circuit is synchronized tothe ventricular pulse generating circuit.

In the pacer disclosed in the aforesaid application, as well as in otherprior art atrial and ventricular pacers, each of the pulse generatingcircuits is free-running in that respective atrial or ventricularstimulating pulses are generated at fixed intervals in the absence ofthe resetting of the pulse generating circuit. The pacer timing issynchronized to the natural heartbeats by controlling the resetting ofthe two circuits upon the detection of each ventricular beat. Whilesystems of this type are satisfactory for implantable pacers, a problemhas been encountered when they are used in connection with externalpacers, that is, pacers which are external to the patient except forelectrical leads.

In an atrial and ventricular demandpacer, each of the pulse generatingcircuits includes a potentiometer which can be adjusted for setting therespective escape interval. Since the pulse generating circuits arefreerunning in the absence of a resetting pulse, it is apparent that ifthe atrial escape interval is less than 50 percent of the ventricularescape interval, then two or more atrial stimulating pulses may begenerated between each pair of ventricular stimulating pulses. Thedetection of a ventricular beat, or the generation of a ventricularstimulating pulse, causes both pulse generating circuits to be reset. Ifthe ventricular escape inter val is N milliseconds and the atrial escapeinterval is less than N/2 milliseconds, since both pulse generatingcircuits are free-running, it is apparent that if a spontaneousventricular beat is not detected prior to the expiration of theventricular escape interval, then at least two atrial stimulating pulseswill be generated. That is because atrial stimulating pulses aregenerated continuously and at fixed time intervals in the absence of thedetection of a spontaneous ventricular beat or the generation of aventricular stimulating pulse. Multiple atrial stimulating pulses, ofcourse, can only produce deleterious effects since the atria should notbe stimulated too close in time to the ventricular beat.

In the case of implantable pacers, where the potentiometer settings areestablished on the production line and are not subject to change, theproblem is not severe because satisfactory production procedures can beemployed for ensuring that multiple stimulating pulses are notgenerated. However, in the case of an external pacer, medical andhospital personnel adjust the various control knobs to vary the twoescape intervals. Especially with poorly trained personnel, the atrialescape interval can be set to be less than 50 percent of the ventricularescape interval, in which case multiple atrial stimulation is possible.

It is a general object of my invention to provide an atrial andventricular pacer in which multiple atrial stimulation is precluded evenwith very short atrial escape intervals.

In accordance with the principles of my invention, the ventricular pulsegenerator is free-running as in prior art pacers. However, the atrialpulse generating circuit is not; instead, it includes a one-shotmultivibrator. The detection of a spontaneous ventricular beat, or thegeneration of a ventricular stimulating pulse, triggers an atrial timingcircuit. At the end of the pre-set atrial escape interval, themultivibrator is tired and an atrial stimulating pulse is generated.Thereafter, the multivibrator returns to the quiescent state; no furtheratrial stimulating pulses are generated. In order for the multivibratorto be triggered once again, a new timing period must be initiated, andthis takes place only when the next spontaneous ventricular beat isdetected or the next ventricular stimulating pulse is generated. Even ifthe atrial escape interval is set to be less than 50 percent of theventricular escape interval, the multivibrator is triggered only oncefor each ventricular beat. Consequently, it is not possible for there tobe multiple atrial stimulations between ventricular beats.

It is a feature of my invention to provide in the atrial pulsegenerating circuit a mechanism for generating only a single atrialstimulating pulse after a predetermined time interval has elapsedfollowing the detection of the last spontaneous beat or the generationof the last ventricular stimulating pulse.

Further objects, features and advantages of my invention will becomeapparent upon consideration of the following detailed description inconjunction with the drawing in which: 1

FIG. 1 is the same as the drawing in my aboveidentified application anddiscloses the circuitry of an atrial and ventricular pacer which canresult in multiple atrialstimulations if care is not takenin insuringthat the atrial escape interval is greater than 50% of the ven tricularescape interval; and

' FIG. 2 depicts an illustrative embodiment of the present invention. 7

Only those parts of the circuit of FIG. 1 will be explained which arerequired for an understanding of the present invention. The pacerincludes a pair of electrodes, El and E2, which are used for ventricularstimulation and a pair of electrodes, E3 and E4, which are used foratrial stimulation. A spontaneous ventricular beat causes a signal toappear on electrodes El and E2, and this signal is processed and resultsin a pulse being applied through capacitor 53 to the base of transistorT6 and through capacitor 54 to the base of transistor T10. (If switch Sis closed, then the pacer operates in a continuous mode and no pulsesare extended to the bases of transistors T6 and T10. Similarly, in thepresence of 60-I-Iz noise, transistors T3 and T4 function to prevent theapplication of pulses to the bases of transistors T6 and T so that thepacer can operate in the continuous mode.) Capacitor 57 normally chargesfrom batteries 1-5 through potentiometer 35, poteniometer 37, andresistors 61 and 63. When the voltage across the capacitor is sufficientto fire transistors T7 and T8, these transistors conduct and a largecurrent flows through them to raise the potential across resistor 63. Atthis time transistor T9 fires and capacitor 65 discharges through thetransistor, the electrodes and the heart tissue to stimulate theventricles. After transistor T9 turns off, capacitor 65 recharges inpreparation for the generation of another stimulating pulse. The settingof potentiometer 35 determines the magnitude of the charging current forcapacitor 57. This, in turn, determines the ventricular escape interval.Each time that the voltage across capacitor 57 is high enough to causetransistors T7 and T8 to fire, the capacitor discharges through them sothat another timing cycle can begin. The duration of the discharge isdetermined by the setting of potentiometer 37. Since a large currentflows through resistor 63 whenever transistors T7 and T8 conduct, it isapparent that the setting of potentiometer 37 determines the width ofthe ventricular stimulating pulse. If a spontaneous ventricular beat isdetected before the expiration of the ventricular escape interval, thentransistor T6 conducts and capacitor 57 discharges through it. In suchan event, the ventricular stimulating pulse which would otherwise havebeen generated when the voltage across capacitor 57 would have reachedthe firing level is not generated. Instead, a new timing cycle begins,with a ventricular stimulating pulse being generated only if theventricular escape interval elapses before the detection of anotherspontaneous ventricular beat.

The atrial pulse generating circuit is very similar to the ventricularpulse generating circuit. Capacitor 58 is the timing capacitor, withpotentiometer 62 being used to adjust the atrial escape interval andpotentiometer 60 being used to adjust the atrial stimulating pulsewidth. Whenever the voltage across capacitor 58 reaches the triggeringlevel transistors T11 and T12 conduct, and a large current flows throughresistor 66. At this time transistor T14 conducts and (through a circuitdifferent from that used in the ventricular pulse generator) an atrialstimulating pulse flows through electrodes E3 and E4. If a spontaneousventricular beat is detected after the previous ventricular beat andprior to the expiration of the atrial escape interval, then the pulsetransmitted through capacitor 54 to the base of transistor T10 controlsthe discharge of capacitor 58. In such a case, an atrial stimulatingpulse is not generated and a new atrial timing period begins. Since itis possible for a premature ventricular beat to occur prior to theexpiration of the atrial escape interval, the detection of a spontaneousventricular beat controls the resetting of the atrial pulse generatoralong with the resetting of the ventricular pulse generator so that thetwo pulse generating circuits are synchronized to each other and to thenatural heart rhythm. Furthermore, in the presence of noise whenspontaneous ventricular beats cannot be detected reliably, thegeneration of a ventricular stimulating pulse causes the atrial pulsegenerating circuit to be reset; when transistors T7 and T8 conduct, apulse is transmitted through diode 36 and resistor 38 to the base oftransistor T10. Thus, at the same time that capacitor 57 dischargesthrough transistors T7 and T8 to control the generation of a ventricularstimulating pulse and the start ofa new ventricular escape timinginterval, capacitor 58 discharges through transistor T10 to control thestart of a new atrial escape timing interval. In this manner the twopulse generating circuits are synchronized to each other even whenspontaneous ventricular beats are not detected (either as a result ofnoise, or the failure of the ventricular beat detecing circuit).

The problem with using the circuit of FIG. 1 for an external pacer inwhich the settings of potentiometers 35 and 62 can be manually adjustedby medical or hospital personnel is that it is possible for the atrialescape interval to be set to be less than 50 percent of the ventricularescape interval. In such a case, consider what happens following thedetection of a spontaneous ventricular beat or the generation of aventricular stimulating pulse. In the former situation, capacitor 57discharges through transistor T6 and in the latter the capacitordischarges through transistors T7 and T8. But in either case, theventricular escape timing interval begins at this time. Also, in bothsituations the base of transistor T10 is pulsed (in the formersituation, through capacitor 54, and in the latter situation, throughdiode 36 and resistor 38) and capacitor 58 discharges through transistorT10. Thus the atrial escape timing interval also begins at this time.Sometime before half of the ventricular escape timing interval haselapsed the potential across capacitor 58 is great enough to firetransistors T11 and T12. At this time an atrial stimulating pulse isgenerated and capacitor 58 discharges through the two transistors. Thecapacitor then starts to charge once again through potentiometer 62 andafter another atrial escape interval has elapsed, a second atrialstimulating pulse is generated. Depending of how low the setting ofpotentiometer 62, two or more stimulating pulses may be generated beforeanother spontaneous ventricular beat is detected or another ventricularstimulating pulse is generated. In either case, the atrial escape timinginterval in progress is interrupted when the next ventricular beat(either spontaneous or stimulated) occurs so that the two pulsegenerators are synchronized to each other. But it is apparent thatmultiple atrial stimulating pulses have been generated to the detrimentof the patient.

In accordance with the principles of my invention, the circuit of FIG. 2has a considerably different atrial pulse generator. Capacitor 58charges through potentiometer 62, the setting of the potentiometerdetermining the atrial escape interval. That end of the capacitorconnected to the emitter of transistor T10 is returned directly toconductor 9, rather than through resistors 64 and 66 as in the circuitof FIG. 1. Potentiometer 60 is not provided in the circuit of FIG. 2because it is potentiometer which determines the width of the generatedpulse.

In the circuit of FIG. 1, the level to which the voltage acrosscapacitor 58 must rise before transistors T11 and T12 turn on isdetermined by the potential of the base of transistor T11. Thispotential, or firing level, is derived by resistors 70, 72 and 74,transistor T13 and diode 76. Capacitor 68 functions as a filter toprevent variations in the firing level as various transients aregenerated in the overall circuit. In the circuit of FIG.

2, transistor T13 and diode 76 are not provided, and the firing level isdetermined by the relative magnitudes of resistors 70, 72 and 74, thebase of transistor T11 being connected to the junction of resistors 72and 74. To minimize the effect of transients, filter capacitor 98 isconnected between the junction of resistors 70 and 72, and conductor 9.

when capacitor 58 fires through transistors T11 and T12, an atrialstimulating pulse is generated. Transistors T11 and T12 do not then turnoff. In the steady state, a small current flows from the batteriesthrough potentiometer 62, transistors T11 and T12, resistor 92,potentiometer 95, and resistors 96 and 97. The current is large enoughto keep transistors T1 1 and T12 on, but it is small enough so that thepotential developed across resistors 97 does not forward bias thebase-emitter junction of transistor T14. The voltage across capacitor 58is equal to the battery voltage minus the drop across potentiometer 62.When transistors T11 and T12 first conduct, as will be described below,current also flows through capacitor 93 and resistor 94. Capacitor 93charges and then discharges until the potential across it is equal tothe potential drop across potentiometer 95, and resistors 96 and 97connected in series. At this time a steady-state condition is reached inwhich there are no voltage variations in the circuit.

As soon as a spontaneous ventricular beat is detected or a ventricularstimulating pulse is generated, transistor T conducts and capacitor 58fully discharges through it. At this time, the voltage acrosstransistors T11 and T12 isnegative (relative to the direction of currentflow through them) since capacitor 93 is charged slightly. Prior to thedischarge of capacitor 58, transistors T15 and T16 are held off becauseno current flows through capacitor 93 and resistor 94 to forward biasthe base-emitter junction of transistor T16; with transistor T16 beingheld off, no base current can flow in transistor T15. As soonastransistors T11 and T12 turn off and no longer deliver current throughpotentiometer 95 and resistors 96 an 97, capacitor 93 discharges throughthese elements and resistor 94. Transistors T15 and T16 still remain offbecause the direction of current flow through resistor 94, as a resultof the discharge of capacitor 93, is in a direction to reverse bias thebase-emitter junction of transistor T16. With transistors T10, T11 andT12 off, capacitor 58 begins to charge through potentiometer 62 from anearzero level as a result of its heavy discharge through transistorT10. As soon as the capacitor voltage rises sufficiently to forward biasthe base-emitter junction of transistor T11 (the time interval for thistaking place being determined by the setting of potentiometer 62, thatis, the atrial escape interval), transistors T11 and T12 conduct andcurrent flows through resistor 92, capacitor 93 and thebase-emitterjunction of transistor T16. The transistor turns on and controls theconduction of transistor T15. When the latter transistor turns on, theadditional current through potentiometer 95 contributes to the chargingof capacitor 93. Current from transistor T15 also flows throughresistors 96 and 97, and the resulting pulse across resistor 97 turns ontransistor T14 to control the application of an atrial stimulating pulseto the atrial electrodes.

As soon as transistors T1 1 and T12 fire, capacitor 93 starts to chargefrom both transistor T12 and transistor T15. Eventually, the currentthrough resistor 94 is so small that transistors T16 and T15 turn off.Capacitor 93 then starts to discharge through potentiometer 95, andresistors 94,96 an 97. The capacitor stops discharging when the-voltageacross it equals the combined drop across potentiometer 95, andresistors 96 and 97 (produced by current flow from transistor T12). Thecombined drop is determined by the potentiometer and the resistormagnitudes. Capacitor 58 no longer can fire transistors T11 and T12because these transistors are already on. The capacitor voltage remainsequal to the battery voltage drop across potentiometer 62. For anotheratrial stimulating pulse to be generated, it is necessary to completelydischarge the capacitor through transistor T10 so that transistors T11and T12 can turn off and capacitor 93 can fully discharge. Thereafter,capacitor 58 starts to charge toward the firing level and when itreaches the firing level an atrial stimulating pulse is generated. Thus,only one atrial stimulating pulse can be generated for each ventricularbeat trigger (turning on of transistor T10).

When transistor T15 first turns on, following the expiration of theatrial escape timing interval when transistors T11 and T12 turn on,collector current from transistor T15 flows through resistors 96 and 97to turn on transistor T14. But collector current also flows throughpotentiometer and capacitor 93 to contribute to the charging of thecapacitor. Thus capacitor 93 is charged not only from the emittercurrent of transistor T12, but also from the collector current oftransistor T15 flowing through potentiometer 95. Transistor T14 conductsonly as long as transistor T15 is on; thus the atrial stimulating pulsewidth is determined by the setting of potentiometer 95 since thepotentiometer impedance determines the time constant of the chargingcircuit which includes capacitor 93.

Not only does the circuit of FIG. 2 allow continuous adjustment of thetwo escape intervals and the pulse widths but in accordance with theprinciples of the invention the atrial escape interval can be made lessthan 50 percent of the ventricular escape interval without producingmultiple atrial stimulations.

Although the invention has been described with reference to a particularembodiment, it is to be under stood that this embodiment is merelyillustrative of the application of the principles of the invention.Numerous modifications may be made therein and other arrangements may bedevised without departing from the spirit and scope of the invention.

What I claim is:

1. An atrial and ventricular pacer comprising ventricular pulsegenerating means for generating a ventricular stimulating pulse forextension to a patients heart following the expiration of a ventricularescape timing interval, means for detecting a spontaneous ventricularbeat of a patients heart or the generation of a ventricular stimulatingpulse for synchronizing said ventricular pulse generating means to thebeating action of the patients heart, timing means responsive to theoperation of said detecting means for measuring an atrial escape timinginterval, means for adjusting the width of said atrial escape timinginterval, means responsive to the expiration of said atrial escapetiming interval for generatingone and only one atrial stimulating pulsefor extension to a patients heart for each single operation of saiddetecting means and independent of the duration of said atrial escapetiming interval, said timing means including a capacitor, first meansfor discharging said capacitor responsive to the operation of saiddetecting means, means for controlling the charging of said capacitorfollowing the discharge thereof, second means conductively connected tosaid first discharging means and responsive to the voltage across saidcapacitor reaching a firing level for discharging said capacitor andcontrolling the operation of said atrial stimulating pulse generatingmeans, and means for maintaining said second discharging meansconducting to hold the voltage across said capacitor below said firinglevel, said second discharging means turning off only after saidcapacitor is discharged by said first discharging means.

2. An atrial and ventricular pacer in accordance with claim 1 whereinsaid ventricular pulse generating means includes means for adjusting thewidth of the respective escape timing interval, and each of said pulsegenerating means includes means for adjusting the width of therespective generated stimulating pulse.

3. An atrial and ventricular pacer comprising ventricular pulsegenerating means for generating ventricular stimulating pulses forextension to a patients heart, means for synchronizing said ventricularpulse generating means to the beating action ofa patients heart, timingmeans for operating in synchronism with the beating action of a patientsheart for measuring an atrial escape timing interval, means foradjusting the width of said atrial escape timing interval, meansresponsive to the expiration of said atrial escape timing interval forgenerating at most one atrial stimulating pulse for extension to apatients heart for each venticular beating action of the patients heartindependent of the duration of said atrial escape timing interval, saidtiming means including a capacitor, first means for discharging saidcapacitor responsive to a beating action of a patients heart, means forcontrolling the charging of said capacitor following the dischargethereof, second means conductively connected to said discharging meansresponsive to the voltage across said capacitor reaching a firing levelfor discharging said capacitor and controlling the operation of saidatrial stimulating pulse generating means, and means for maintainingsaid second discharging means conducting to hold the voltage across saidcapacitor below said firing level, said second discharging means turningoff only after said capacitor is discharging by said first dischargingmeans.

4. An atrial and ventricular pacer in accordance with claim 3 whereinsaid atrial pulse generating means includes means for adjusting thewidth of the generated atrial stimulating pulse following the expirationof said atrial escape timing interval.

5. An atrial and ventricular pacer in accordance with claim 3 whereinsaid width adjusting means of said atrial escape timing interval isadjustable to produce an escape interval less than 50 percent of thetime interval separating successive stimulating pulses generated by saidventricular pulse generating means.

1. An atrial and ventricular pacer comprising ventricular pulsegenerating means for generating a ventricular stimulating pulse forextension to a patient''s heart following the expiration of aventricular escape timing interval, means for detecting a spontaneousventricular beat of a patient''s heart or the generation of aventricular stimulating pulse for synchronizing said ventricular pulsegenerating means to the beating action of the patient''s heart, timingmeans responsive to the operation of said detecting means for measuringan atrial escape timing interval, means for adjusting the width of saidatrial escape timing interval, means responsive to the expiration ofsaid atrial escape timing interval for generating one and only oneatrial stimulating pulse for extension to a patient''s heart for eachsingle operation of said detecting means and independent of the durationof said atrial escape timing interval, said timing means including acapacitor, first means for discharging said capacitor responsive to theoperation of said detecting means, means for controlling the charging ofsaid capacitor following the discharge thereof, second meansconductively connected to said first discharging means and responsive tothe voltage across said capacitor reaching a firing level fordischarging said capacitor and controlling the operation of said atrialstimulating pulse generating means, and means for maintaining saidsecond discharging means conducting to hold the voltage across saidcapacitor below said firing level, said second discharging means turningoff only after said capacitor is discharged by said first dischargingmeans.
 2. An atrial and ventricular pacer in accordance with claim 1wherein said ventricular pulse generating means includes means foradjusting the width of the respective escape timing interval, and eachof said pulse generating means includes means for adjusting the width ofthe respective generated stimulating pulse.
 3. An atrial and ventricularpacer comprising ventricular pulse generating means for generatingventricular stimulating pulses for extension to a patient''s heart,means for synchronizing said ventricular pulse generating means to thebeating action of a patient''s heart, timing means for opErating insynchronism with the beating action of a patient''s heart for measuringan atrial escape timing interval, means for adjusting the width of saidatrial escape timing interval, means responsive to the expiration ofsaid atrial escape timing interval for generating at most one atrialstimulating pulse for extension to a patient''s heart for eachventicular beating action of the patient''s heart independent of theduration of said atrial escape timing interval, said timing meansincluding a capacitor, first means for discharging said capacitorresponsive to a beating action of a patient''s heart, means forcontrolling the charging of said capacitor following the dischargethereof, second means conductively connected to said discharging meansresponsive to the voltage across said capacitor reaching a firing levelfor discharging said capacitor and controlling the operation of saidatrial stimulating pulse generating means, and means for maintainingsaid second discharging means conducting to hold the voltage across saidcapacitor below said firing level, said second discharging means turningoff only after said capacitor is discharging by said first dischargingmeans.
 4. An atrial and ventricular pacer in accordance with claim 3wherein said atrial pulse generating means includes means for adjustingthe width of the generated atrial stimulating pulse following theexpiration of said atrial escape timing interval.
 5. An atrial andventricular pacer in accordance with claim 3 wherein said widthadjusting means of said atrial escape timing interval is adjustable toproduce an escape interval less than 50 percent of the time intervalseparating successive stimulating pulses generated by said ventricularpulse generating means.